12 numbers
4 objects taken 4 at a time is "4!" This is read "4 factorial" and is 1*2*3*4=24 One fourth of them, or 6, of these numbers are going to start with 0, so they have to be removed. The answer is 18. {4067, 4076, 4607, 4670, 4706, 4760, 6047, 6074, 6407, 6470, 6704, 6740, 7046, 7064, 7406, 7460, 7604, 7640} ■
If you want 4-digit numbers, there are 24 of them.
With a total of 90,000 five digit numbers, we can conclude that there is 45,000 EVEN five digit numbers.
9
With 123 digits you can make 123 one-digit numbers.
12 numbers
Not sure what a "didget" is. It is possible to make 18 5-digit numbers.
8
720 of them.
162
5040
6, as long as they are all different
12,13,14 21,23,24 31,32,34 43,42,41 12 two-digit numbers
There are no three didgit numbers but there are 63 three digit numbers.
24 if you don't repeat any numbers.24
10999